Head-up display technology has progressed rapidly in recent years. Compact, fixed-reference head-up display systems are now installed in automobiles. Virtual-reality (VR) and mixed-reality (MR) goggles for the consumer market are also available. Nevertheless, various impediments to user-friendly head-up display technology remain. One challenge relates to the increased size, weight, cost and power consumption of redundant optical componentry in a fixed-reference head-up display system or wearable display device.